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June 28, 2014

For stars, it’s more about nature than nurture. The evolution of most stars is controlled mainly by the circumstances of their birth — and particularly their weight. Massive stars “age” more quickly than less-massive ones, so they live shorter lives.

A good example is Alphecca, the crown jewel of the northern celestial crown. It stands almost straight overhead a couple of hours after sunset.

Alphecca is actually two stars. They were born at the same time, from the same cloud of gas and dust. But one of the stars is almost three times as massive as the other — and that’s the key to their fate.

A star shines by “fusing” atoms in its core. Gravity squeezes the core of a heavier star more tightly, heating the core and revving up the nuclear reactions.

A star spends most of its life fusing its original hydrogen fuel to make helium — the prime of a star’s life, known as the main sequence.

According to models of how stars evolve, Alphecca’s heavier star should remain on the main sequence for about 850 million years. Its companion, on the other hand, should remain in that phase for more than 12 billion years.

There’s a caveat, though. The stars of Alphecca are quite close together. As the heavier star reaches the end of its time on the main sequence it will expand, perhaps dumping some of its gas on its companion. That could alter the smaller star’s evolution — and change the time it spends in the prime of life.

Script by Damond Benningfield, Copyright 2014

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